Cardiac rhythm management system with user interface for threshold test

ABSTRACT

An implantable cardiac rhythm management system includes a user interface, such as an external programmer, for performing therapy energy threshold tests. The threshold tests allow the caregiver to determine the threshold energy at which paces capture the heart, i.e., cause a resulting contraction of the heart chamber to which the paces are delivered. The programmer provides recorded indications of the energy corresponding to each paced event, so that the caregiver can easily determine the point at which capture was lost. This recorded representation of pacing energy makes it easy for the caregiver to determine proper pacing thresholds to be used to ensure adequate pacing, while minimizing energy drain to prolong the useful life of the implanted device.

CROSS-REFERRENCE TO RELATED APPLICATION(S)

[0001] This application is a continuation of U.S. Pat. application Ser.No. 09/378,106, filed on Aug. 20, 1999, the specification of which ishereby incorporated by reference.

TECHNICAL FIELD

[0002] The present system relates generally to cardiac rhythm managementsystems and particularly, but not by way of limitation, to a cardiacrhythm management system providing, among other things, a user interfacefor threshold testing.

BACKGROUND

[0003] When finctioning properly, the human heart maintains its ownintrinsic rhythm, and is capable of pumping adequate blood throughoutthe body's circulatory system. However, some people have irregularcardiac rhythms, referred to as cardiac arrhythmias. Such arrhythmiasresult in diminished blood circulation. One mode of treating cardiacarrhythmias uses drug therapy. Anti-arrhythmic drugs are often effectiveat restoring normal heart rhythms. However, drug therapy is not alwayseffective for treating arrhythmias of certain patients. For suchpatients, an alternative mode of treatment is needed. One suchalternative mode of treatment includes the use of a cardiac rhythmmanagement system. Such systems often include portions that areimplanted in the patient and deliver therapy to the heart.

[0004] Cardiac rhythm management systems include, among other things,pacemakers, also referred to as pacers. Pacers deliver timed sequencesof low energy electrical stimuli, called pace pulses, to the heart, suchas via an intravascular leadwire or catheter (referred to as a “lead”)having one or more electrodes disposed in or about the heart. Heartcontractions are initiated in response to such pace pulses (this isreferred to as “capturing” the heart). By properly timing the deliveryof pace pulses, the heart can be induced to contract in proper rhythm,greatly improving its efficiency as a pump. Pacers are often used totreat patients with bradyarrhythmias, that is, hearts that beat tooslowly, or irregularly.

[0005] Cardiac rhythm management systems also include cardioverters ordefibrillators that are capable of delivering higher energy electricalstimuli to the heart. Defibrillators are often used to treat patientswith tachyarrhythmias, that is, hearts that beat too quickly. Suchtoo-fast heart rhythms also cause diminished blood circulation becausethe heart isn't allowed sufficient time to fill with blood beforecontracting to expel the blood. Such pumping by the heart isinefficient. A defibrillator is capable of delivering an high energyelectrical stimulus that is sometimes referred to as a defibrillationcountershock. The countershock interrupts the tachyarrhythmia, allowingthe heart to reestablish a normal rhythm for the efficient pumping ofblood. In addition to pacers, cardiac rhythm management systems alsoinclude, among other things, pacer/defibrillators that combine thefunctions of pacers and defibrillators, and any other implantable orexternal systems or devices for diagnosing or treating cardiacarrhythmias.

[0006] One problem faced by cardiac rhythm management systems isdetermining whether the therapy delivered has had its desired effect.For example, after implanting a pacer in a patient, a physician or othercaregiver would like to know if the pace pulses being delivered areeffective at “capturing the heart,” i.e., evoking a contraction of theheart chamber to which the pace pulse was delivered. If the paces arenot succeeding at capturing the heart, the physician will likely programa higher energy pace pulse to obtain capture. In order to save energy,prolonging the useful life of the implanted device before replacement isrequired, lower energy paces are preferable provided that the physicianis assured that the lower energy pace pulses will capture the heart.Replacement of the implanted device carries significant expense as wellas some risk of discomfort and/or complications.

[0007] In order to determine the appropriate energy of pacing therapy,the physician typically programs several different therapy energy levels(i.e., pacing voltage amplitude, pacing pulsewidth, or combination ofamplitude and pulsewidth) to see what energy levels appropriately obtaincapture. Because proper therapy energy levels are critical in providingeffective cardiac rhythmn management therapy and extending the usefullife of the implanted device, there is a need for techniques that assistthe physician or other caregiver in determining threshold energies forcardiac rhythm management therapy.

SUMMARY OF THE INVENTION

[0008] This document describes, among other things, portions of cardiacrhythm management system including a user interface for performingtherapy energy threshold tests. In one embodiment, the user interfaceincludes a programmer that provides recorded indications of the energycorresponding to paced events, so that the caregiver can easilydetermine the point at which capture was lost. This recordedrepresentation of pacing energy makes it easy for the caregiver todetermine proper pacing thresholds to be used to ensure adequate pacing,while minimizing energy drain to prolong the useful life of theimplanted device.

[0009] In one embodiment, the cardiac rhythm management system includesan external user interface. The user interface includes a communicationmodule, adapted for remote communicative coupling to the implantabledevice. The user interface also includes a threshold testing module. Theuser interface provides a recorded output indicator of energy associatedwith an instance of therapy delivery by the implantable device.

[0010] This document also describes a method that includes pacing apatient at varying energies and recording a separate output indicator ofenergy associated with each pace. These and other aspects of the presentsystem and methods will become apparent upon reading the followingdetailed description and viewing the accompanying drawings that form apart thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the drawings, like numerals describe substantially similarcomponents throughout the several views. Like numerals having differentletter suffixes represent different instances of substantially similarcomponents.

[0012]FIG. 1 is a schematic drawing illustrating generally oneembodiment of portions of a cardiac rhythm management system and anenvironment in which it is used.

[0013]FIG. 2 is a schematic drawing illustrating generally oneembodiment of a cardiac rhythm management device coupled by leads to aheart.

[0014]FIG. 3 is a schematic diagram illustrating generally oneembodiment of portions of a cardiac rhythm management device coupled toheart.

[0015]FIG. 4 illustrates generally one embodiment of a screen displayassociated with an external programmer or other user interface.

[0016]FIG. 5 is an example of a strip chart recording provided by aprinter associated with a programmer.

[0017]FIG. 6 is an example of a strip chart recording, similar to FIG.5, in which the output indicators provide recorded indications of pacingpulsewidth, rather than amplitude, during pacing threshold testing.

DETAILED DESCRIPTION

[0018] In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims and their equivalents. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. Like numerals having different lettersuffixes represent different instances of substantially similarcomponents. In this document, “and/or” refers to non-exclusive “or”(e.g., “A and/or B” includes each of “A but not B,” “B but not A,” and“A and B”).

[0019] The present methods and apparatus will be described inapplications involving implantable medical devices including, but notlimited to, implantable cardiac rhythm management systems such aspacemakers, cardioverter/defibrillators, pacer/defibrillators, andbiventricular or other multi-site coordination devices. However, it isunderstood that the present methods and apparatus may be employed inunimplanted devices, including, but not limited to, external pacemakers,cardioverter/defibrillators, pacer/defibrillators, biventricular orother multi-site coordination devices, monitors, programmers andrecorders.

General System Overview and Examples

[0020] This document describes, among other things, a cardiac rhythmmanagement system with a user interface for a threshold test. FIG. 1 isa schematic drawing illustrating generally, by way of example, but notby way of limitation, one embodiment of portions of a cardiac rhythmmanagement system 100 and an environment in which it is used. In FIG. 1,system 100 includes an implantable cardiac rhythm management device 105,also referred to as an electronics unit, which is coupled by anintravascular endocardial lead 110, or other lead, to a heart 115 ofpatient 120. System 100 also includes an external user interface, suchas programmer 125, providing wireless communication with device 105using a communication module such as telemetry device 130. Catheter lead110 includes a proximal end 135, which is coupled to device 105, and adistal end 140, which is coupled to one or more portions of heart 115.

[0021]FIG. 2 is a schematic drawing illustrating generally, by way ofexample, but not by way of limitation, one embodiment of device 105coupled by leads 11 OADocket B to heart 115, which includes a rightatrium 200A, a left atrium 200B, a right ventricle 205A, a leftventricle 205B, and a coronary sinus 220 extending from right atrium200A. In this embodiment, atrial lead 110A includes electrodes(electrical contacts) disposed in, around, or near an atrium 200 ofheart 115, such as ring electrode 225 and tip electrode 230, for sensingsignals and/or delivering pacing therapy to the atrium 200. Lead 11 OAoptionally also includes additional electrodes, such as for deliveringatrial and/or ventricular cardioversion/defibrillation and/or pacingtherapy to heart 115.

[0022] In FIG. 2, a ventricular lead llOB includes one or moreelectrodes, such as tip electrode 235 and ring electrode 240, fordelivering sensing signals and/or delivering pacing therapy. Lead 11 OBoptionally also includes additional electrodes, such as for deliveringatrial and/or ventricular cardioversion/defibrillation and/or pacingtherapy to heart 115. Device 105 includes components that are enclosedin a hermetically-sealed can 250. Additional electrodes may be locatedon the can 250, or on an insulating header 255, or on other portions ofdevice 105, for providing unipolar pacing and/or defibrillation energyin conjunction with the electrodes disposed on or around heart 115.Other forms of electrodes include meshes and patches which may beapplied to portions of heart 115 or which may be implanted in otherareas of the body to help “steer” electrical currents produced by device105. In one embodiment, one of atrial lead I1OA or ventricular lead 110Bis omitted, i.e., a “single chamber” device is provided, rather than thedual chamber device illustrated in FIG. 2. In another embodiment,additional leads are provided for coupling device 105 to other heartchambers and/or other locations in the same heart chamber as one or moreof leads 11OA-B. The present method and apparatus will work in a varietyof configurations and with a variety of electrical contacts or“electrodes.”

Example Cardiac Rhythm Management Device

[0023]FIG. 3 is a schematic diagram illustrating generally, by way ofexample, but not by way of limitation, one embodiment of portions ofdevice 105, which is coupled to heart 115. Device 105 includes a powersource 300, an atrial sensing circuit 305, an atrial therapy circuit310, a ventricular sensing circuit 315, a ventricular therapy circuit320, and a controller 325.

[0024] Atrial sensing circuit 305 is coupled by atrial lead 11OA toheart 115 for receiving, sensing, and/or detecting electrical atrialheart signals. Such atrial heart signals include atrial activations(also referred to as atrial depolarizations or Pwaves), which correspondto atrial contractions. Such atrial heart signals include normal atrialrhythms, and abnormal atrial rhythms including atrial tachyarrhythmias,such as atrial fibrillation, and other atrial activity. Atrial sensingcircuit 305 provides one or more signals to controller 325, via node/bus327, based on the received atrial heart signals.

[0025] In one embodiment, atrial therapy circuit 310 provides atrialpacing therapy, as appropriate, to electrodes located at or near one ofthe atria 200 of heart 115 for obtaining resulting evoked atrialdepolarizations. In a further embodiment, atrial therapy circuit 310also provides cardioversion/defibrillation therapy, as appropriate, toelectrodes located at or near one of the atria 200 of heart 115, forterminating atrial fibrillation and/or other atrial tachyarrhythmias.

[0026] Ventricular sensing circuit 315 is coupled by ventricular lead11OB to heart 115 for receiving, sensing, and/or detecting electricalventricular heart signals, such as ventricular activations (alsoreferred to as ventricular depolarizations or Rwaves), which correspondto ventricular contractions. Such ventricular heart signals includenormal ventricular rhythms, and abnormal ventricular rhythms, includingventricular tachyarrhythmias, such as ventricular fibrillation, andother ventricular activity. Ventricular sensing circuit 315 provides oneor more signals to controller 325, via node/bus 327, based on thereceived ventricular heart signals.

[0027] In one embodiment, ventricular therapy circuit 320 providesventricular pacing therapy, as appropriate, to electrodes located at ornear one of the ventricles 205 of heart 115 for obtaining resultingevoked ventricular depolarizations. In a further embodiment, ventriculartherapy circuit 320 also provides cardioversion/defibrillation therapy,as appropriate, to electrodes located at or near one of the ventricles205 of heart 115, for terminating ventricular fibrillation and/or otherventricular tachyarrhythmias.

[0028] Controller 325 controls the delivery of therapy by atrial therapycircuit and/or ventricular therapy circuit 320 and/or other circuits,based on heart activity signals received from atrial sensing circuit 305and ventricular sensing circuit 315, as discussed below. Controller 325includes various modules, which are implemented either in hardware or asone or more sequences of steps carried out on a microprocessor or othercontroller. Such modules are illustrated separately for conceptualclarity; it is understood that the various modules of controller 325need not be separately embodied, but may be combined and/or otherwiseimplemented, such as in software/firmware.

[0029] In general terms, sensing circuits 305 and 315 sense electricalsignals from heart tissue in contact with the catheter leads 110A-B towhich these sensing circuits 305 and 315 are coupled. Sensing circuits305 and 315 and/or controller 325 process these sensed signals. Based onthese sensed signals, controller 325 issues control signals to therapycircuits, such as ventricular therapy circuit 320, if necessary, for thedelivery of electrical energy (e.g., pacing and/or defibrillationpulses) to the appropriate electrodes of leads 11OA-B. Controller 325may include a microprocessor or other controller for execution ofsoftware and/or firmware instructions. The software of controller 325may be modified (e.g., by remote external programmer 125) to providedifferent parameters, modes, and/or functions for the implantable device105 or to adapt or improve performance of device 105.

[0030] In one further embodiment, one or more sensors, such as sensor330, may serve as inputs to controller 325 for adjusting the rate atwhich pacing or other therapy is delivered to heart 115. One such sensor330 includes an accelerometer that provides an input to controller 325indicating increases and decreases in physical activity, for whichcontroller 325 increases and decreases pacing rate, respectively.Another such sensor includes an impedance measurement, obtained frombody electrodes, which provides an indication of increases and decreasesin the patient's respiration, for example, for which controller 325increases and decreases pacing rate, respectively. Any other sensor 330providing an indicated pacing rate can be used.

Example Threshold Test

[0031] Device 105 includes, among other things, a pacing threshold testmodule included in software and/or hardware of controller 325. Using anicon on the screen display of external programmer 125, the physician orother caregiver initiates a pacing threshold test mode that allowsobservation of the effectiveness of varying therapy energy levels atcapturing the heart, i.e., at obtaining a resulting contraction of theheart chamber to which the energy is delivered. Energy levels are variedby changing either the amplitude or the pulsewidth of the deliveredpacing pulse. During the threshold test, data is communicated from theimplanted device 105 to the external user interface, e.g., programmer125, using real-time telemetry by device 105 in response tosynchronization pulses provided by programmer 125.

[0032] In one embodiment, amplitude is varied by changing the pacingamplitude to 5.0 V for four paces, then stepping the energy down by 0.5V increments for each successive four paces down to a pacing amplitudeof 3.0 V. After that, the pacing amplitude continues to decrease by 0.2V increments, for each successive four paces, until the pacing amplitudereaches 0.2V. As the pacing amplitudes are decreased, the caregiverobserves on the screen display of programmer 125 a correspondingelectrogram signal, i.e., a cardiac signal associated with theparticular chamber of the heart to which the pace pulses are delivered.If the caregiver notices that the pacing pulses being delivered fail tocapture the heart (i.e., the characteristic depolarization is absentafter the pace pulse is delivered), the caregiver ends the thresholdtest, such as by using an icon on the user interface. When the caregiverends the threshold test, the user interface displays the last pacingamplitude delivered before capture was lost. The caregiver can then setthe pacing amplitude to that value, or alternatively, the caregiver canadd an appropriate “safety margin” when setting the pacing amplitude.

[0033] During the pacing threshold test, the previously programmedpacing parameters (amplitude, pulsewidth, rate, AV delay, etc.) arestored. In one embodiment, after the pacing threshold test is ended,pacing continues at either the previously stored pacing parametervalues, or at default values that are regarded as safe enough to ensurecapture (e.g., 5.0 V amplitude, 0.5 millisecond pulsewidth). After apacing threshold test is conducted for a particular chamber, thecaregiver can retest pacing amplitudes. In one embodiment, a retest ofpacing thresholds begins at the default initial values (e.g., amplitudeof 5.0 V or pulsewidth of 0.5 milliseconds). In another embodiment,however, a retest of pacing thresholds begins at a predetermined numberof increments (e.g., 3 increments) above the energy level before whichcapture was lost. For example, if a first threshold test usingamplitudes lost capture at 0.4 V, as determined by the physician endingthe threshold test, then, the screen display would indicate 0.6 V as thethreshold voltage before which capture was lost. In this example, aretest of pacing thresholds would begin at 1.2 V, that is, at 3increments of 0.2 V above the previous minimum capture amplitude of 0.6V. By starting a retest of pacing thresholds at a predetermined numberof increments above the result of the previous test, the time requiredfor conducting a retest is reduced.

[0034] In one embodiment, the pacing amplitudes or pulsewidths areautomatically stepped down (decremented) every fourth pace. In anotherembodiment, the pacing amplitudes or pulsewidths are manuallydecremented or incremented by the physician using the “+” and “−” iconson the screen display of programmer 125 and illustrated in FIG. 4.

Example Programmer Interface

[0035]FIG. 4 illustrates generally, by way of example, but not by way oflimitation, one embodiment of a screen display associated with externalprogrammer 125. The screen display of FIG. 4 includes visual images ofcardiac signals obtained from one or more implanted or externalelectrodes, such as surface electrodes and/or bipolar or unipolar atrialor ventricular implanted electrodes. The screen display also includesvarious icons, including an icon for starting/ending the threshold test.The threshold test is alternatively ended by removing the telemetrydevice 130 (e.g., wand) from near the implanted device 105 to interruptcommunication therebetween. In threshold testing mode this screendisplay also includes information regarding the particular chamber beingtested, the present amplitude of pace pulses being delivered (or thelast pacing amplitude before loss of capture, after the threshold testis ended), and/or the present pacing pulsewidth.

[0036] The above-described threshold testing technique provides only oneexample of carrying out a threshold test to determine pacing thresholds.In an alternative embodiment, the pacing energy is varied by decreasingpacing pulsewidths (the duration of the pacing pulse) rather than bydecreasing pacing amplitude. In another embodiment, either of amplitudeor pulsewidth are increased, rather than decreased, until capture isobtained. Moreover, it is understood that the caregiver can select whichelectrodes are associated with a particular pacing threshold test, sothat separate pacing thresholds are determined, for example, for atrial,ventricular, or other electrodes, or for unipolar or bipolar pacingconfigurations.

[0037] Returning to the above-described embodiment of decreasing pacingamplitudes to determine pacing threshold energies, it is apparent thatthe pacing threshold test is conducted “real time.” The accuracy of thedetermined pacing threshold depends on the caregiver ending thethreshold test when loss of capture is observed. However, otherdistractions, for example, may result in a less than adequate responsetime of the caregiver in ending the test. Moreover, proper medicalrecordkeeping may require that the physician records the test. For theseand other reasons, programmer 125 includes a printer that provides astrip chart recording of the threshold test. Furthermore, programmer 125also includes a screen display that also displays the information thatis displayed by the recorded strip chart. In one embodiment, programmer125 also includes a storage device (e.g., magnetic disk storage) thatalso stores the same data that is recorded on the strip chart.

Example Recorded Output

[0038]FIG. 5 is an example of a strip chart recording provided by theprinter associated with programmer 125. Based at least in part on datatelemetered from implanted device 105 to external programmer 125, thestrip chart recording provides real time electrograms of cardiac signalsassociated with one or more implanted or surface electrode sites. In theembodiment illustrated in FIG. 5, the strip chart includes cardiacsignals from a surface electrogram 500, an atrial electrogram 505, and aventricular electrogram 510. These signals include cardiacdepolarizations that allow the caregiver to determine whether theparticular heart chamber has contracted in response to a delivered paceof a particular energy.

[0039] The strip chart of FIG. 5 also includes atrial and ventricularevent markers 515A-Z, indicated by upwardly pointing arrows. Thesearrows indicate the occurrence of a pace, delivered by atrial therapycircuit 310 or ventricular therapy circuit 320, or of a sensed cardiacdepolarization, detected by atrial sensing circuit 305 or ventricularsensing circuit 315. Below corresponding event markers, the strip chartincludes text describing information related to the particular eventmarker. “AS” indicates that the associated event marker corresponds toan atrial sense, “AP” indicates that the associated event markercorresponds to an atrial pace. Similarly, “VS” indicates that theassociated event marker corresponds to a ventricular sense, “VP”indicates that the associated event marker corresponds to a ventricularpace. Other markers also exist. A corresponding numeral indicates thetime interval in milliseconds since the previous event marker in thesame chamber. The strip chart of FIG. 5 also includes output indicators520A-J, based on data telemetered from the implanted device 105, of theenergies associated with particular pace pulses. In FIG. 5, becauseatrial amplitude is being varied to determine atrial pacing thresholds,the output indicators of atrial amplitudes are printed below theircorresponding event markers (e.g., output indicator 520A of 5.OVcorresponds to atrial pace event marker 515F, output indicator 520B of5.OV corresponds to atrial pace event marker 515H, etc.). In oneembodiment, these output indicators of pacing amplitudes are alsodisplayed on a screen display of programmer 125. In a furtherembodiment, these output indicators of pacing amplitudes are also storeddigitally in storage media associated with programmer 125.

[0040] By providing a recorded representation of electrograms, pacingevent markers, and associated pacing amplitudes (or pulsewidths), thecaregiver is more easily able to determine the particular pacing energyat which capture is lost. The energy at which capture is lost isdetermined by locating the particular event markers which are notfollowed by a substantially immediate cardiac depolarization associatedwith the particular chamber of the heart to which the pacing energy isbeing delivered. The strip chart conveniently provides a representationof the pacing energy (e.g., amplitude or pulsewidth) that is easilyreferred to each corresponding pace, in this case, by being printeddirectly below the event marker associated with that pace. This recordedrepresentation of pacing energy makes it easy for the caregiver todetermine proper pacing thresholds to be used to ensure adequate pacing,while minimizing energy drain to prolong the useful life of implanteddevice 105.

[0041]FIG. 6 is an example of a strip chart recording, similar to FIG.5, in which the output indicators 600A-J provide recorded indications ofpacing pulsewidth for a pacing threshold test that varies pacing energyby varying pacing pulsewidth, rather than amplitude. In FIG. 6, becauseatrial pacing pulsewidth is being varied to determine atrial pacingthresholds, the output indicators of atrial pulsewidth are printed belowtheir corresponding event markers (e.g., output indicator 600A of 0.5milliseconds corresponds to atrial pace event marker 515E, outputindicator 600B of 0.5 milliseconds corresponds to atrial pace eventmarker 515G, etc.).

[0042] In one embodiment, programmer 125 automatically selects theappropriate electrogram (e.g., atrial or ventricular) to be displayed onthe screen display of programmer 125 during the threshold test, based onthe particular chamber for which thresholds are being tested) if thatelectrogram is not already being displayed on the screen display ofprogrammer 125. In another embodiment, the screen display of electrogramcorresponding to the chamber being tested for pacing thresholdsautomatically provides an enlarged view of that electrogram during thethreshold test of that chamber. This makes it convenient for thecaregiver to view small, not easily discemable evoked responseartifacts. This makes it easy, for example, for the physician to see ifa P-wave results from an atrial pace at a particular energy, otherwisethe P-wave may be quite difficult to see.

[0043] Conclusion This document describes, among other things, portionsof a cardiac rhythm management system including a user interface forperforming therapy energy threshold tests. In one embodiment, the userinterface includes recorded indications of the energy corresponding topaced events, so that the caregiver can easily determine the point atwhich capture was lost. This recorded representation of pacing energymakes it easy for the caregiver to determine proper pacing thresholds tobe used to ensure adequate pacing, while minimizing energy drain toprolong the useful life of the implanted device.

[0044] It is to be understood that the above description is intended tobe illustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. For example, although aspects of the present system havebeen described with respect to threshold testing of pacing thresholds,it is understood that the user interface could provide similar usefuloperation during testing of defibrillation thresholds. In anotherexample, the recorded output indicator of therapy energy need not beprovided as a printed output; such recorded output can also be storedelectronically, such as together with corresponding electrograms andevent markers, for subsequent viewing on the screen display of theprogrammer or elsewhere. Other variations are also possible. The scopeof the invention should, therefore, be determined with reference to theappended claims, along with the full scope of equivalents to which suchclaims are entitled.

What is claimed is:
 1. A cardiac rhythm management system including anexternal user interface, the user interface including: a communicationmodule, adapted for remote communicative coupling to the implantabledevice; a threshold testing module, adapted for initiating therapydelivery by the implantable device at energies that vary between one ormore instances of therapy delivery by the implantable device; and arecorded output indicator of energy associated with an instance oftherapy delivery by the implantable device.
 2. The system of claim 1,further including a therapy marker associated with an instance oftherapy delivery by the implantable device.
 3. The system of claim 2,further including a representation of a cardiac signal acquired by theimplantable device.
 4. The system of claim 3, in which at least one ofthe output indicator of energy and the therapy marker is associated witheach instance of therapy delivery by the implantable device.
 5. Thesystem of claim 4, further including a printer providing at least one ofthe output indicator of energy, the therapy marker, and therepresentation of the cardiac signal.
 6. The system of claim 5, furtherincluding an implantable cardiac rhythm management device, adapted forcommunicative coupling to the user interface.
 7. The system of claim 6,further including a leadwire adapted for coupling the cardiac rhythmmanagement device to a patient.
 8. The system of claim 2, furtherincluding a screen display, and in which the representation of thecardiac signal being acquired appears on the screen display and isenlarged during threshold testing from the view displayed when thresholdtesting is not being conducted.
 9. The system of claim 2, furtherincluding a screen display, and in which the representation of thecardiac signal, which corresponds to a chamber in which thresholds arebeing tested, is enlarged during threshold testing.
 10. The system ofclaim 1, in which the threshold testing module automatically variespacing energies during the threshold test.
 11. The system of claim 1, inwhich the threshold testing module varies pacing energies during thethreshold test based on user commands.
 12. A cardiac rhythm managementsystem including a remote user interface, the user interface including:a telemetry module, adapted for communicative coupling to theimplantable device; a threshold testing module, adapted for initiatingpacing therapy delivery by the implantable device at energies that varybetween one or more paces; and a printer, providing a printout includingan electrogram, markers of paced and sensed events, and a separateindicator of energy associated with each of the paced markers.
 13. Amethod including: pacing a patient at varying energies; and recording aseparate output indicator of energy associated with each pace.
 14. Themethod of claim 13, in which recording includes printing a strip chartincluding an electrogram, markers of paced and sensed events, and aseparate indicator of the energy associated with each of the pacedmarkers associated with pacing the patient at varying energies.
 15. Themethod of claim 14, in which the indicator includes a pace amplitude.16. The method of claim 14, in which the indicator includes a pacepulsewidth.
 17. The method of claim 14, further including displaying ona programmer screen display the electrogram, the markers of paced andsensed events, and the separate indicator of the energy of each of thepaced markers associated with pacing the patient at varying energies.18. The method of claim 17, further including enlarging the electrogramon the screen display during threshold testing.
 19. The method of claim17, further including selecting the electrogram to correspond to thechamber being paced at varying energies, if that electrogram isn'talready being displayed.
 20. The method of claim 13, further includingautomatically varying the pacing energies during the threshold testbased on a predetermined algorithm.
 21. The method of claim 13, furtherincluding varying the pacing energies during the threshold test based onat least one user command.